avfilter/dnn_backend_openvino: Fix free context at random place

It will be freed again by ff_dnn_uninit.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
Reviewed-by: Wenbin Chen <wenbin.chen@intel.com>
Reviewed-by: Guo Yejun <yejun.guo@intel.com>

libavfilter/dnn/dnn_backend_openvino.c

@@ -959,7 +959,6 @@ err:
     if (input_model_info)
         ov_preprocess_input_model_info_free(input_model_info);
 #endif
-    dnn_free_model_ov(&ov_model->model);
     return ret;
 }